The present invention relates to the field of delivery of electrical impulses (and/or fields) to bodily tissues for therapeutic purposes, and more specifically to devices and methods for treating conditions associated with bronchial constriction
There are a number of treatments for various infirmities that require the destruction of otherwise healthy tissue in order to affect a beneficial effect. Malfunctioning tissue is identified, and then lesioned or otherwise compromised in order to affect a beneficial outcome, rather than attempting to repair the tissue to its normal functionality. While there are a variety of different techniques and mechanisms that have been designed to focus lesioning directly onto the target nerve tissue, collateral damage is inevitable.
Still other treatments for malfunctioning tissue can be medicinal in nature, in many cases leaving patients to become dependent upon artificially synthesized chemicals. Examples of this are anti-asthma drugs such as albuterol, proton pump inhibitors such as omeprazole (Prilosec), spastic bladder relievers such as Ditropan, and cholesterol reducing drugs like Lipitor and Zocor. In many cases, these medicinal approaches have side effects that are either unknown or quite significant, for example, at least one popular diet pill of the late 1990's was subsequently found to cause heart attacks and strokes.
Unfortunately, the beneficial outcomes of surgery and medicines are, therefore, often realized at the cost of function of other tissues, or risks of side effects.
The use of electrical stimulation for treatment of medical conditions has been well known in the art for nearly two thousand years. It has been recognized that electrical stimulation of the brain and/or the peripheral nervous system and/or direct stimulation of the malfunctioning tissue, which stimulation is generally a wholly reversible and non-destructive treatment, holds significant promise for the treatment of many ailments.
Electrical stimulation of the brain with implanted electrodes has been approved for use in the treatment of various conditions, including pain and movement disorders including essential tremor and Parkinson's disease. The principle behind these approaches involves disruption and modulation of hyperactive neuronal circuit transmission at specific sites in the brain. As compared with the very dangerous lesioning procedures in which the portions of the brain that are behaving pathologically are physically destroyed, electrical stimulation is achieved by implanting electrodes at these sites to, first sense aberrant electrical signals and then to send electrical pulses to locally disrupt the pathological neuronal transmission, driving it back into the normal range of activity. These electrical stimulation procedures, while invasive, are generally conducted with the patient conscious and a participant in the surgery.
Brain stimulation, and deep brain stimulation in particular, is not without some drawbacks. The procedure requires penetrating the skull, and inserting an electrode into the brain matter using a catheter-shaped lead, or the like. While monitoring the patient's condition (such as tremor activity, etc.), the position of the electrode is adjusted to achieve significant therapeutic potential. Next, adjustments are made to the electrical stimulus signals, such as frequency, periodicity, voltage, current, etc., again to achieve therapeutic results. The electrode is then permanently implanted and wires are directed from the electrode to the site of a surgically implanted pacemaker. The pacemaker provides the electrical stimulus signals to the electrode to maintain the therapeutic effect. While the therapeutic results of deep brain stimulation are promising, there are significant complications that arise from the implantation procedure, including stroke induced by damage to surrounding tissues and the neurovasculature.
One of the most successful modern applications of this basic understanding of the relationship between muscle and nerves is the cardiac pacemaker. Although its roots extend back into the 1800's, it was not until 1950 that the first practical, albeit external and bulky pacemaker was developed. Dr. Rune Elqvist developed the first truly functional, wearable pacemaker in 1957. Shortly thereafter, in 1960, the first fully implanted pacemaker was developed.
Around this time, it was also found that the electrical leads could be connected to the heart through veins, which eliminated the need to open the chest cavity and attach the lead to the heart wall. In 1975 the introduction of the lithium-iodide battery prolonged the battery life of a pacemaker from a few months to more than a decade. The modern pacemaker can treat a variety of different signaling pathologies in the cardiac muscle, and can serve as a defibrillator as well (see U.S. Pat. No. 6,738,667 to Deno, et al., the disclosure of which is incorporated herein by reference).
Another application of electrical stimulation of nerves has been the treatment of radiating pain in the lower extremities by means of stimulation of the sacral nerve roots at the bottom of the spinal cord (see U.S. Pat. No. 6,871,099 to Whitehurst, et al., the disclosure of which is incorporated herein by reference).
The smooth muscles that line the bronchial passages are controlled by a confluence of vagus and sympathetic nerve fiber plexuses. Spasms of the bronchi during asthma attacks and anaphylactic shock can often be directly related to pathological signaling within these plexuses. Anaphylactic shock and asthma are major health concerns.
Asthma, and other airway occluding disorders resulting from inflammatory responses and inflammation-mediated bronchoconstriction, affects an estimated eight to thirteen million adults and children in the United States. A significant subclass of asthmatics suffers from severe asthma. An estimated 5,000 persons die every year in the United States as a result of asthma attacks. Up to twenty percent of the populations of some countries are affected by asthma, estimated at more than a hundred million people worldwide. Asthma's associated morbidity and mortality are rising in most countries despite increasing use of anti-asthma drugs.
Asthma is characterized as a chronic inflammatory condition of the airways. Typical symptoms are coughing, wheezing, tightness of the chest and shortness of breath. Asthma is a result of increased sensitivity to foreign bodies such as pollen, dust mites and cigarette smoke. The body, in effect, overreacts to the presence of these foreign bodies in the airways. As part of the asthmatic reaction, an increase in mucous production is often triggered, exacerbating airway restriction. Smooth muscle surrounding the airways goes into spasm, resulting in constriction of airways. The airways also become inflamed. Over time, this inflammation can lead to scarring of the airways and a further reduction in airflow. This inflammation leads to the airways becoming more irritable, which may cause an increase in coughing and increased susceptibility to asthma episodes.
Two medicinal strategies exist for treating this problem for patients with asthma. The condition is typically managed by means of inhaled medications that are taken after the onset of symptoms, or by injected and/or oral medication that are taken chronically. The medications typically fall into two categories; those that treat the inflammation, and those that treat the smooth muscle constriction. The first is to provide anti-inflammatory medications, like steroids, to treat the airway tissue, reducing its tendency to over-release of the molecules that mediate the inflammatory process. The second strategy is to provide a smooth muscle relaxant (an anti-cholinergic and/or anti-adrenergic medication) to reduce the ability of the muscles to constrict.
It has been highly preferred that patients rely on avoidance of triggers and anti-inflammatory medications, rather than on the bronchodilators as their first line of treatment. For some patients, however, these medications, and even the bronchodilators are insufficient to stop the constriction of their bronchial passages, and more than five thousand people suffocate and die every year as a result of asthma attacks.
Anaphylaxis likely ranks among the other airway occluding disorders of this type as the most deadly, claiming more than eight thousand deaths per year in the United States alone. Anaphylaxis (the most severe from of which is anaphylactic shock) is a severe and rapid systemic allergic reaction to an allergen. Minute amounts of allergens may cause a life-threatening anaphylactic reaction. Anaphylaxis may occur after ingestion, inhalation, skin contact or injection of an allergen. Anaphylactic shock usually results in death in minutes if untreated. Anaphylactic shock is a life-threatening medical emergency because of rapid constriction of the airway. Brain damage sets in quickly without oxygen. Anaphylactic shock itself accounts for approximately 1,500 deaths every year in the United States.
The triggers for these fatal reactions range from foods (nuts and shellfish), to insect stings (bees), to medication (radiocontrasts and antibiotics). It is estimated 1.3 to 13 million people in the United States are allergic to venom associated with insect bites; 27 million are allergic to antibiotics; and 5-8 million suffer food allergies. All of these individuals are at risk of anaphylactic shock from exposure to any of the foregoing allergens. In addition, anaphylactic shock can be brought on by exercise. Yet all are mediated by a series of hypersensitivity responses that result in uncontrollable airway occlusion driven by smooth muscle constriction, and dramatic hypotension that leads to shock. Cardiovascular failure, multiple organ ischemia, and asphyxiation are the most dangerous consequences of anaphylaxis.
Anaphylactic shock requires advanced medical care immediately. Current emergency measures include rescue breathing; administration of epinephrine; and/or intubation if possible. Rescue breathing may be hindered by the closing airway but can help if the victim stops breathing on his own. Clinical treatment typically consists of antihistamines (which inhibit the effects of histamine at histamine receptors) which are usually not sufficient in anaphylaxis, and high doses of intravenous corticosteroids. Hypotension is treated with intravenous fluids and sometimes vasoconstrictor drugs. For bronchospasm, bronchodilator drugs such as salbutamol are employed.
Given the common mediators of both asthmatic and anaphylactic bronchoconstriction, it is not surprising that asthma sufferers are at a particular risk for anaphylaxis. Still, estimates place the numbers of people who are susceptible to such responses at more than 40 million in the United States alone.
Tragically, many of these patients are fully aware of the severity of their condition, and die while struggling in vain to manage the attack medically. Many of these incidents occur in hospitals or in ambulances, in the presence of highly trained medical personnel who are powerless to break the cycle of inflammation and bronchoconstriction (and life-threatening hypotension in the case of anaphylaxis) affecting their patient.
Unfortunately, prompt medical attention for anaphylactic shock and asthma are not always available. For example, epinephrine is not always available for immediate injection. Even in cases where medication and attention is available, life saving measures are often frustrated because of the nature of the symptoms. Constriction of the airways frustrates resuscitation efforts, and intubation may be impossible because of swelling of tissues.
Typically, the severity and rapid onset of anaphylactic reactions does not render the pathology amenable to chronic treatment, but requires more immediately acting medications. Among the most popular medications for treating anaphylaxis is epinephrine, commonly marketed in so-called “Epi-pen” formulations and administering devices, which potential sufferers carry with them at all times. In addition to serving as an extreme bronchodilator, epinephrine raises the patient's heart rate dramatically in order to offset the hypotension that accompanies many reactions. This cardiovascular stress can result in tachycardia, heart attacks and strokes.
Unlike cardiac arrhythmias, which can be treated chronically with pacemaker technology, or in emergent situations with equipment like defibrillators (implantable and external), there is virtually no commercially available medical equipment that can chronically reduce the baseline sensitivity of the muscle tissue in the airways to reduce the predisposition to asthma attacks, or to break the cycle of bronchial constriction associated with an acute asthma attack or anaphylaxis.
Accordingly, there is a need in the art for new products and methods for treating the immediate symptoms of anaphylactic shock and asthma.